let s1 = Symbol();
let s2 = Symbol();
console.log(s1, s2,
	s1 == s2,
	typeof s1,
	typeof s2);

s1 = Symbol('imooc');
s2 = Symbol('imooc');
console.log(s1, s2,
	s1 == s2,
	typeof s1,
	typeof s2);

let s = Symbol({ name: 'imooc' });
console.log(s, s.description);
let obj = {
	[s]: 1,
	s: 2,
	[s1]: 3,
	[s2]: 3
}
console.log(obj, obj[s]);

for (let key in obj) {
	console.log(obj[key])
}
console.log(Object.getOwnPropertySymbols(obj),
	Object.keys(obj),
	Object.getOwnPropertyNames(obj),
	JSON.stringify(obj));

s1 = Symbol.for('imooc');
s2 = Symbol.for('imooc');
console.log(s1, s2,
	s1 === s2,
	s1 === Symbol.for('imooc'),
	Symbol.keyFor(s1));
